Xamarin Android模拟器在滚动视图中使用网格，仅绘制网格的第一页

Question

我正在使用标准 Android 模拟器在 Visual Studio 2019 中开发 Xamarin Forms 应用。 XAML 包含一个包含 Grid 的 ScrollView。网格只有两列。我有一个用于连接到数据库的 OnStart 事件的处理程序，获取包含 64 个对象的响应，将两个标签添加到每个对象的网格中，并填充标签。 ScrollView 的背景颜色设置为黄色。当我使用模拟器调试应用程序时，初始屏幕绘制正确。但是当我向下滚动时，网格没有被填充。背景仍然是黄色的，表明滚动视图的大小是正确的（或者至少，大到足以容纳更多的标签）。我做错了什么？

当我在第二个 for 循环的底部放置断点时，添加标签后，我看到我拥有所有我期望的标签对象，并且它们的文本属性设置符合我的期望。

这是 XAML：

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="CapsBases.MainPage">

    <ScrollView BackgroundColor="Yellow"
                VerticalOptions="FillAndExpand">
        <Grid Margin="10"
              x:Name="BasesGrid">
            <!-- two columns:  base ID and status -->
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="60" />
                <ColumnDefinition Width="*" />
            </Grid.ColumnDefinitions>

        </Grid>
    </ScrollView>
</ContentPage>

事件处理程序调用 MainPage.xaml.cs 文件中名为 ShowBases() 的函数。这里是：

public async void ShowBases()
{
    string url = "http://10.0.2.2:5000/caps/bases";
    //HttpClient client = new HttpClient();
    //string info = await client.GetStringAsync(url);
    //// await DisplayAlert("Coil Count", message, "Close");
    //// The base ID and string will be returned in a single string with a space separating them.
    //string[] pieces = info.Split(' ');
    //BaseID.Text = pieces[0];
    //BaseStatus.Text = pieces[1];
    using (HttpClient client = new HttpClient())
    {
        HttpResponseMessage response = await client.GetAsync(url);
        if (response.IsSuccessStatusCode)
        {
            string data = await response.Content.ReadAsStringAsync();
            //IEnumerable<Base> baseList = JsonConvert.DeserializeObject<IEnumerable<Base>>(data);
            List<Base> baseList = JsonConvert.DeserializeObject<List<Base>>(data).OrderBy(b =>b.BaseName).ToList();
            //BaseID.Text = theBase.BaseName;
            //BaseStatus.Text = theBase.Status;
            string message = $"Retrieved {baseList.Count()} bases.";
            await DisplayAlert("Result", message, "Close");

            Grid theGrid = BasesGrid;
            var rowDefinitions = theGrid.RowDefinitions;
            for (int i = 0; i < baseList.Count(); i++)
            {
                RowDefinition rowDef = new RowDefinition { Height = 20 };
                rowDefinitions.Add(rowDef);
            }

            await DisplayAlert("Row count", $"The grid has {BasesGrid.RowDefinitions.Count()} rows.", "Close");

            // We have the grid with all the rows we need.  Now we have to create a label for each grid cell.

            try
            {
                for (int i = 0; i < baseList.Count(); i++)
                {
                    BasesGrid.Children.Add
                    (
                        new Label
                        {
                            Text = baseList[i].BaseName,
                            HorizontalOptions = LayoutOptions.Start
                        },
                        0, i
                    );
                    BasesGrid.Children.Add
                    (
                        new Label
                        {
                            Text = baseList[i].Status,
                            HorizontalOptions = LayoutOptions.Start
                        },
                        1, i
                    );
                }
            }
            catch (Exception ex)
            {
                await DisplayAlert("Error", $"Failed to add row data: {ex.Message}", "Close");

            }
        }
        else
        {
            await DisplayAlert("Get Coils failure",
                                $"Failed to retrieve coils; status code: {response.StatusCode}",
                                "Close");
        }
    }

}

}

Answer 1

在垂直方向的 StackLayout 中围绕网格。 Grid 没有在 ScrollView 内展开。